High-voltage vacuum-tube system



May 29, 1928. 1,671,204

A. A. OSWALD HIGH VOLTAGE VACUUM TUBE SYSTEM Filed May 25, 1922 4 Sheets-Sha e; 1

//'7 vema/z' Ar/hur A. Gawa/a.

May 29, 1928.

A. A. OSWALD HIGH VOLTAGE VACUUM TUBE SYSTEM Filed May 23. 1922 May 29, 1928. 1,671,204

A. A. OSWALD HIGH VOLTAGE VACUUM TUBE SYSTEM Filed 1922 :5

. May 29. 1928. 1,671,204

A A. OSWALD HIGH VOLTAGE VACUUM TUBE SYSTEM Filed May 25. 1922 4 Sheets-Sheet 4 64 g 14? #11. n \FIS I l O 5.2

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hue/flan Ari/7w ,4. OSM/a/a by my Patented May 29, 1928.

UNITED STATES PATENT OFFICE.

ARTHUR A. OSWALD, OF BRADLEY BEACH, NEW JERSEY, ASSIGNOR TO WESTERN ELEC- TRIO COMPANY, INCORPORATED, OF NEW YORK, N. Y., A CORPORATION OF NEW YORK.

.HIGH-VOLTAGE VACUUM-TUBE SYSTEM.

Application filed May 23, 1922. Serial No. 562,973.

This invention relates to high voltage vacuum tube amplifier and similar systems which amplify such large energies that a circulating cooling fluid is employed to dis- 5 sipate the heat generated by the vacuum tubes of the system.

The system described herein as embodying the various features of the invention comprises a two-stage amplifier system for amplifying radio frequency waves consisting of a band of frequencies of the width of a speech frequency band. The energy to be amplified may for example, consist of one side band of a modulated wave having a frequency of 75,000 cycles per second. The upper side band in that case comprises frequencies from about 75,200 cycles to 77,000 cycles per second. The first amplifier stage consists of a relatively low power Water cooled amplifier with an input of about 1/2 kw. and an output of approximately 5 kw., while the second high power stage employs or'more similar vacuum tubes in parallel, with a combined output of high frequency energy of about 200 kw. or upward. Both amplifier stages employ vacuum tubes having an external metallic anode around which the cooling fluid circulates. In this type of system it is essential that the cooling fluid continue at all times to circulate properly in order to prevent the generation 0 steam or the .occurrence of some other dangerous condition which might lead to damage to the apparatus or injury to the operator. Hence, the present invention has for its general object the provision of such safety arrangements and alarm devices as will tend to protect the system from undesirable conditions by automatically shutting off the power of the system. or giving an alarm, or both. To this end is provided a control circuit which will during normal operation hold in closed position a relay. This relay being released operates a circuit breaker and cuts off the power from the entiresystem. Provision is made for opeiiing or grounding the control circuit on the occurrence of any one of several abnormal co ditior s. this manner fill? h ld ng I? lay is operated and the circuit breaker opened. Some abnormal conditions guarded against are: excessive plate current in any tube, failure of the grid polarizing current source, failure of the cooling water to flow in sufficient volume, and too high a temperature of the outgoing cooling water.

(perta n features of the invention are claimed in applicants applications Serial No. 560,518, filed May -12, 1922, and Serial No. 699,431, filed March 15, 1924.

The present invention has for an object the provision of a safe arrangement for measuring the direct current component of the spacecurrent of any individual one of a group of tubes of the system by means of a single ammeter.

Various other novel features of importance will appear from the following detailed description.

The desired objects are attained by means of the apparatus and circuits hereinafter described in detail in connection with the accompanying drawings,wherein Fig. 1 is a simplified circuit diagram of the amplifier system; Figs. 2 and 3 together, Fig. 3 bein placed to the right of Fig. 2, constitute ii more complete circuit diagram with linessential details omitted and certain mechanical elements diagrammatically indicated;

f Fig. 4; is asemi-diagrammatic section taken so through Fig. 3 on the line X-X; and Fig.

5 is a side view partly in section taken at right angles to Fig. 4:, showing the actual arrangement of a panel unit of the amplifier B containing ten tubes.

As shown in Fig. 1, the amplifier consists of a first or low power stage A of which the output circuit leads into a second or high power stage B which in turn supplies waves of high power to the antenna circuit C. The waves to be amplified are applied to the input circuit of the amplifier A across the terminal 1 and ground connection 2. The output circuit of the amplifier A extends from the anode elements of the vacuum tubes of the amplifier A through the primary of transformer 3 and a large by-passing and st pp g ond n er t to g n c rcuit connection 4 leads to the positive terminal of the plate current source 9. The secondary of the transformer 3 is shunted by the usual input resistance 5 and is included in circuit between the grid elements of the tubes of the amplifier B and the ground connection 2. The output: circuit of the amplitier B extends from the anode elements through condensers 6 which pass the high frequency component and relays 7 which pass the direct current component through a two-branched path to ground. The first branch is for the direct current supply and includes the high frequency choke coil 8 and the high voltage direct current supply source 9 which has a terminal voltage of the order of 10,000 volts or more. The high frequency branch extends through condenser 10 and the primary of the high frequency transformer 11 which has its secondary in the antenna circuit or in a circuit coupled to the antenna circuit in any suitable way if desired. The source 12 is a mechanical generator or equivalent means for maintaining the grids of the tubes of both the stages A and B at a suitable negative potential which may be regulated by resistances 13 and 14:. Filters F serve to eliminate commutator fluctuations from the potential applied to the grids. The vacuum tube cathodes are heated by alternating current supplied from a suitable source through a system of transformers 15. The midpoints of the secondaries of these transformers are grounded. The grid and anode elements are connected to the ground ed midpoints. Relays 7 are marginal relays which. remain unoperated on normal space current but operate on abnormal space current for a purpose hereinafter described.

.In the more complete circuit diagram of Figs. 2 and 3, the elements of Fig. 1 are as sociated with various other apparatus eonsisting in general of water cooling arrangements, control circuit arrangements, and alarm circuit arrangements. The input circuit of the low power amplifier A extends from the terminal 1 through an input resistance and filter F which consists of any desired number of sections having shunt capacity and series inductance to the ground connection 2. The output circuit is from the anode elements 16 through the primary of transformer 3 through the main coil switch circuit breaker l7 and the high voltage plate current source 9 to ground. A low impedance high frequency path'through condenser 4 to ground may be provided.

The input circuit of the amplifier B extends from the grids of the tubes of this amplifier through the secondary of transformer 3 which is shunted by a high resistance and a filter F to ground. The grid polarizing source 12 supplies both systems of vacuum tubes and also energizes a control circuit to be referred to in detail hereinafter. The grid supply circuit extends from the negative side of the generator 12 through the resistances 13 and 14.- to round. The direct current plate supply circuit of the tubes of the system B extends from ground at the mid point of the secondary of transformer 15 (in Fig. 3) to the tube cathodes, thence to the anodes 19, marginal relays 7, jacks 20, high frequency choke coil 8, circuit breaker 17 and source 9 to ground. The high frequency path is the same as that just traced with the exception that the relays 7 are shunted by condensers 6 and the high frequency current instead of going through the choke coil 8, passes through condenser 10 and high frequency transformer 11 to ground, thereby impressing high voltage radio frequency waves on the antenna circuit C. There is thus supplied to the antenna circuit,scvcral hundred kw. of high frequency energy of the same wave form as is impressed upon the input terminals 1, 2. The input energy may be only a fraction of a kw.

In order to dissipate the heat generated in the vacuum tubes, tubes of the external anode type are used, these being cooled by continuous circulation of water about their external surfaces. In the amplifier A, the water supply proceeds from an input supply through the pipe 21 and a coil 22 consisting of several feet of rubber hose. After circulating around the tubes, the heated water flows away through a similar coil 22 and outlet pipe 23 to a pressure controlled water alarm system 24 which controls a contact device, 25.

The device 24 is controlled by the flow of water through the outlet pipe 23 so that when water stops flowing or flows at a slower rate, the device 25 is rotated a fraction of a revolution in a clockwise direction. The pipe 23 has a regulating valve 26 around which is a constricted by-pass 27. There are connections to two water filled chambers 28 and 29. The lower portion of these chambers is connected by a tube 30. The tube 30 and the lower portion of the chambers are filled with mercury. Vhen the water is not flowing, the mercury stands at the same levels in the chambers 28 and 29. Then water flows, the pressure at the top of the chamber 29 becomes greater than the pressure at the top of the chamber 28 and causes some mercury to flow through the tube 30 into the chamber 28. As the chamber 28 is of much larger cross sectional area than the chamber 29, this causes a float 31 which rides upon the surface of the mercury in the chamber 29 to move downwardly a relatively large distance and rotate the contact controlling device 25 in a counter clockwise direction. As shown, water is assumed to be flowing at a, normal rate.

The'description of the devices 24 and 25 ture rises above a predetermned desired value, contacts will be established for a purpose mentioned later. The oil switch circuit breaker 17 is arranged to keep the plate supply circuit from the high voltage source 9 closed so long as the coil 34 is energized. The coil 34 may be in circuit with any convenient source such as a battery, the filament supply source or the negative grid supply generator. The operation of the system Wlll be essentially the same regardless of what source energizes the coil 34. For convenience, it is assumed to be energized by a circuit from the negative terminal of the grid supply source 12, through a regulating resistance, the armature 35, contact 36 and coil 34 to ground So long as the generator 12 supplies a proper voltage and the armature 35 remains on contact 36, the circuit breaker 17 will be held closed. When these conditions no longer exist, the circuit breaker will open. However, it will be seen that if the coil 34 is energized by a battery or other source independent of the generator 12, nevertheless the circuit breaker 17 will be opened when the negative grid voltage sup ply fails for any reason or the source 12 becomes inoperative. It is understood, of course, that the effect of gravity. on the armature 35 is to hold the contacts 35, 36 separated.

A control circuit extends from the negative terminal of the grid polarizing source 12 through the regulating resistances 37 and 38, contacts 39, contacts 40, contacts 41, contacts 42, conductor 43 and winding 44 to ground. Winding 44, when energized through the circuit just traced, holds the armature 35 against the contacts 36 and thus maintains power on the plate circuits of the tubes. If the control circuit just traced is broken at any point or at any of the contacts through which it passes, or is grounded at any point, circuit breaker 17 will operate and cut off the power. Several push buttons 45 are arranged at strategic points about the installation so that attendants may ground the control circuit by operating one of these buttons and cut oil the power. There is another contact 46 for grounding the control circuit through a conductor 47 and, as will be described hereinafter, the use of conductor 47 and contact 46 is optional, and they may be omitted without interfering with the proper functioning of any other element of the system. The amplifier B may comprise additional panels or banks of amplifying tubes in addition to those shown cooled by the same or separate water supply.

It should be understood that the control circuit just traced may extend through any number of contacts similar to contacts 39 and 49 'or other contacts which may be opened by abnormal conditions or intentionally by an attendant.

The contacts 39 will be insulated from each other by rotation of the device 25 in case the water supply of the amplifier B falls below a predetermined minimum rate of flow. The contacts 40 will be opened by abnormal space current through any tube of] the right-hand or left-hand series respectively, of the amplifier B. The arrangements for accomplishing this will be de scribed in the next paragraph. The contacts 41 will be opened by excessive space current in either of the tubes of the amplitier A. The contacts 42 will be insulated from each other in the case of insuflicient flow of cooling water in the outlet pipe 23 of amplifier A. Any of these occurrences or the establishment of a ground connection at contacts 45 or 46 will deenergize the main control circuit through the coil 44 and allow the armature 35 to fall back from the contact 36. Arrangements to cause quick action of the armature 35 are desirable. For this purpose, a circuit from the resistance 38 through a marginal relay 48, resistance 49, and coil 50 to ground through coil 44, is provided. When the main holding circuit is closed at all points, the path through relay 48, resistance 49 and coil 59 is short-circuited so that only a negligible amount of current flows therethroughf In order that the current may be entirely negligible under such conditions, the coil 50 is grounded through the coil 44 instead of being directly grounded. Now, let it be supposed that the main holding circuit is opened at any contact as, for example, contacts 39. A substantial current will at once flow through the winding of relay 48 and the windings 50 and 44 to ground. The winding 50 has a much larger number of turns than the winding 44 and exercises a much greater pull on the armature 35. T he armature 35 is thereupon quickly separated from contact 36. A' ground connection established at any of the contacts 45 will also deenergize winding 44 and allow armature 35 to fall back from contact 36. In this case, however, the winding 50 will not be energized and the action will be slower. The relay winding 44 is so adjusted that it holds its armature on small current but requires considerably more current in order to initially pick up the armature. Resistance 38 is so adjusted with respect to the ill-ii potential of source 12 and the adjustment of relay winding 44, thatwhen the winding 44 has allowed the armature 35 to be sep arated' from the contact 36, the armature will not be picked up again until a master push button or switch 51 is operated to short circuit the resistance 38. It is, therefore, practically impossible for the contacts 35 and 36 to be separated and restored again before the circuit breaker 17 has operated. A momentary grounding or breaking of the control circuit is therefore snfiicient to bring about operation of the circuit breaker 17 and prevent its restoration until the master circuit 51 is operated. If the system is not operating and any abnormal condition exists which is maintaining the control circuit open or if any of the contacts 45 are closed, it is imposible to close the circuit breaker 17 and begin operation until the abnormal condition has been remedied because, in this case, closure of the master control switch 51 will not cause the armature 35 to make contact at 36.

The arrangements for opening the contacts 40 will now be described. In the circuit for direct current to the anode of each tube is a marginal relay 7 The relays 7 do not pick up their armatures 52 on normal space current but are so adjusted as to pick up only on current of some predetermined value above normal. When only armature 52 is operated, a spring or gravityoperated pivoted element 53 moves against a small projecting lever 54: pivoted on a shaft 55. The element 53 when released rotates the shaft 55 sufliciently to cause a projecting arm 56 to break the contact 40. In practice, the shaft 55 may carry a rotary element similar to the device 25 with contacts similar to the contacts 39 which are separated when the shaft 55 is rotated and which take the place of the contact 40. The relays 7 are practically at plate potential and are hence at a high potential with respect to ground. It is, therefore, dangerone to approach these relays for manual op eration. The shaft 55 is therefore made of insulating material and is elongated sufliciently to extend out through a front panel board 57 By manipulation of the knob 58 it is therefore possible to safely restore any or all of the elements 53 when the armatures 52 have become deenergized. For this reason the elements 53 can safely be restored even though at the same time the master switch 51 is closed. In the amplifier A are contacts 41 which correspond in function to the contacts 40. The control circuit includes the contacts 41 which are normally closed. If either of the tubes of amplifier A is taking excessive space current, the corresponding marginalrelay 79 opens a contact 41 which breaks the control circuit. The relays 79 are in the direct current path which extends from the cathodes of the tubes of amplifier A through relay 79, an ammeter 63, winding of relay and the choke coil 81. The function of the relay 80 is described hereinafter.

The vacuum tube anodes are at high p0 tcntial with respect to ground. It is desirable to insulate these anodes from the water supply system which is done by leading in the water through a coil 22 of rubber hose or erpiivalent insulating material. A coil of fi teen or twenty feet of such rubber hose-or tubing when filled with water of ordinary purity is found to have a resistance of a million ohms or more so that the desired insulation is accomplished. 1

The amplifier B, in general, will comprise a large number of tubes, since individual tubes of sufficient power capacity have not yet been developed. It is desirable to measure the plate currents of these tubes individually at times as this furnishes a convenient method of determining in advance the probability of failure of a particular tube. Since the plate side of the tube circuits is at high potential and the various anodes are connected to each other conductively by the metallic piping system 59, the problem of measuring the individual space current of the various tubes with safety to the operator and without providing a separate meter for each tube, which would be expensive, is solved by an arrangement now to be described. The input and output supply pipes to the Water containing cooling chamber surrounding each anode are made metallically discontinuous and for the discontinuous portion is substituted a short length of about one or two inches of rubber hose or tubing 60. Such a short length has been found to have a resistance when filled with water of about 2000 ohms. This insures that if an ammeter is connected in the circuit of a particular tube it will measure only the current of that tube since the resistance of the meter and its asso ciated series circuit will be negligible in comparison with the resistance of the rubber tube sections 60. A series of jacks 20 is provided, each jack being normally closed. A circuit extends from each anode 19 through relay '7 which consists of a few turns of negligible resistance, conductor 61, a ack 20 to the common plate circuit bus bar 62. By opening any jack 20, the ammeter 63 is inserted in the direct current plate circuit of thecorresponding tube and will indlcate the direct current component flowing through that tube. Since the contacts of the jacks 20 and the ammeter 63 are practically at anode potential, that is, 10,000 volts .or more above ground otential, it would not be. safe to approach t ese or operate them in the ordinary manner. A handle 64 of insulating material which is at least a. foot in length terminates in a conductive tip 65 which, when inserted in any jack, connects the ammeter in circuit. A series of holes registering with the various jacks are 10- eated in the front panel board 57. The plate currents of the various tubes may thus be measured and observed without danger to the operator.

The filamentary cathodes are heated by alternating current. Preferably all the cathodes in the system are heated from the same A. C. generator or power line, as for example, the generator 66. Generator 66 has circuit connections to the primary of a suitable number of filament heating transformers 15. The secondaries of transformers 15 are connected across the filament systems in shunt to condensers 67. The condensers 67 serve to by-pass high frequency currents aroundthe secondaries of transformers 15. In the system A, regulating resistances are employed in the circuits of the primaries of transformers 15. In system B, however, each filament has an individual regulating resistance. 'One half of the filaments of the system B are connected through their regulating resistances to one side of the secondary circuit of the transformers 15 while the other half are connected through their regulating resistances to the other side of the circuit. This results in a better balance of the filament circuit with respect to the middle or ground point of the transformers 15.

The filaments of high power tubes-such as used in the present system dissipate a large amount of energy. Mcansare provided for giving an alarm in case the filaments are energized when the cooling water is not flowing. For this purpose a control circuit en ergized by the filament circuit is provided.

A transformer 68 is shunted across the filament heating circuit. The secondary of transformer 68 has one side grounded and the other side extends through conductor 69, alarm bell 70 and conductor 71 to each of the contacts 72, to ground, .which will 'be closed when the water is not flowing. Nonflow of water therefore in either cooling system will cause the bell 70 to ring if the filament current is turned on. In case the marginal relay 48 is energized to pick up its armature, another contact 73 is closed which causes the bell 70 to ring. An alarm is thus given in case the oil switch circuit breaker control relay is caused to operate by opening the main control circuit in the manner hereinbefore described, since this is the condition which results in the marginal relay 48 being energized to pick up its armature.

In case the thermometers or thermostats 32 and 33 register a temperature of the outfiowing water which is high enough to make a contact, another circuit is closed through the secondary of transformer 68,conductor 69, relay 74and conductor 75 to ground at the particular thermometer which registers the excessively high temperature. This en- .ergizes the relay 74and causes it to pick up its armature. A circuit is then closed through the secondary of transformer 68 through the bell 78 to ground through contact 77. This last occurrence not only gives an alarm but grounds the main control circuit through the dotted line circuit connection 47 and the armature 46 of the relay 74. The circuit breaker 17 is thereby operated and the alarm 76 continues to sound so long as thermometer 32 or thermometer 33 reg istcrs excessive water temperature. The condenser 78 may be provided to prevent sparking across the armature contacts of relay 74.

A further feature is electrically driven clocks PC and FC which register the total time the plate current and filament current respectively are turned on in the system. These clocks are so arranged that they run only during the time in which they are energized by current. The filament clock F0 is directly energized from the filament circuit through the conductor 69 and a secondary of transformer 68. Direct current flowing in the plate circuits of the tubes of amplifier A passes to ground through circuits containing the marginal relays 79, the plate clock controlling relay 80 and the alternating eurrent choke coil 81. When direct current is flowing through the relay 80, its armature is picked up establishing a contact at 82. This contact closes a circuit through the plate clock PC from the secondary of transformed 68, conductor 69 and an armature 82. By observing the clocks at suitable intervals, a record may be kept of the total time of current flow through the plate and filament circuits. An ammeter 90 in circuit with condenser 91 is shunted around the coil 80 and the'coil 81. The current flowing through the ammeter 90 is a component corresponding to the amplitude variation frequency of the plate current of the tubes of the amplifier A and if the ammeter 90 is properly calibrated it indicates the percentage of modulation of the outgoing Wave. The average negative grid voltage is so adjusted as to cause partial rectification of the high frequency Wave in the plate circuit. This produces variations in the plate circuit current which correspond to the frequency of the amplitude variations of a speech or other modulated wave or side band wave which is being amplified. The path to ground through condensers 67 is of high impedance to these variations as is also the path through the coil winding 80 and choke coil 81. Condenser 91 is large (about 40 microfarads) and offers a low impedance path to these variations which therefore are by-passed to ground through ammeter 90.

the arrows which show the direction of flow.

For cooling purposes, water may be supplied from an ordinary city water supply system although the inventlon contemplates the employment of other equivalent fluids for coolingpurposes with a pump, if necessary, for creating a proper flow and a cooling tank or its equivalent if the same fluid is to be continually circulated. Relays 7 with their armatures 52 and the associated elements 53 and 54 are placed adjacent their respective tubes in the manner indicated. The anodes 19 extend through any suitable water-tight sealing arrangement 84 and are joined to the upper glass portion 85 of the vacuum tube. The exact relation and position of the filament 86 and grid 87 is not shown in the drawing which is diagrammatic in this respect. It is contemplated that the upper portion of the filament be about on a level with the upper portion of the cooling chamber so that the heat from the filaments will be readily dissipated in the surrounding water. The anodes 19 are connected to the metallic wall 88 of the cooling chamber by spring cli s 89 which make contact with the anodes wlien they are positioned within cooling chambers. The metallic wall 88 is, therefore, for practical purposes, to be regarded as the anode terminal of the tube within the chamber.

For use in high power radio transmission, it is contemplated that the input terminals 1, 2 will be connected to any suitable source of modulated waves or other waves which are to be radiated. However, the present amplifying system is well adapted for use in any instance where low power alternating wave energy is to be amplified to produce high power alternating wave energy of similar wave form. It should be understood that the present system as herein described may be modified in many respects to meet operating conditions without departure from the essential principles of the invention. In particular, it should be pointed out that the use of several banks of amplifiers connected in parallel in the amplifier B is contemplated. As many units, each comprising ten or more tubes. may be employed as desired. The anode bus bar 62 and the grid bus bar 89 will be extended to the additional banks of tubes, each of which will be provided with the accessory apparatus shown and a grounded source for heating the filaments. The main control circuit Will be controlled by apparatus 24 and 25 and contacts 40, 42, 45 and 46 corresponding to each unit.

Fig. 5 is aside View partly in section of a panel of the amplifier B having ten tubes mounted thereon. The tubes are mounted, five on a side, in two rows in the water jackets 88. The hose coils 22 are coiled on the central support 92 resting on insulators 93. The piping system 59 together with the water jackets 88 are mounted on a centrally located mounting board 94 which is supported by insulators 95 on an element of the steel frame 96 which supports the entire arrangement. The arrangement of the elongated rod 55 and the relays 7 together with their associated parts is clearly indicated. The position of jacks 20 with respect to the front panel board 57 is indicated. .The panel board contains a series of filament circuit rheostats 97 and such other auxiliary apparatus (not shown) as may be necessary or advisable.

The bus bar 62 for plate current supply has a terminal on the insulator 98. Bus bar 89 serves for attachment tothe grids of the various tubes and has a terminal attachment on the insulator 99. One side of each filament is directly connected to a filament bus bar 100. The other side of each filament is connected to a binding post 102 from which a connection will be made through a filament circuit rheostat 97 for each filament in the usual manner. The connections to the filament circuit rheostats are not shown in Fig. 5. I

In operation, a proper flow of cooling water will be established. The main control circuit will not be energized unless a proper negative grid voltage is supplied from source 12. This prevents the system from being started up without a negative grid voltage which would result in an excessive rush of current through the tube. The filament heating source 66 is set in operation.

Closure of the master push button or switch filenergizes the master control circuit 37, 39, 40, 40, 41, 41, 42 and relay Winding 44 to ground. This establishes a circuit through the Winding 34 of the oil switch circuit breaker and closes the plate circuit. The waves to be amplified are then applied to the input terminals 1, 2 and radiated from the antenna circuit C at high ower. The operation will then continue and t e various elements function in a manner which will be well understood from the preceding description so long as no abnormal condition exists in the system. Shutting down may be accomplished by pressing the push button 45, cutting oil the filament heating circuit and stopping the generator 12. The I alarm bell does not ring when the system is shut down in this manner. It is not possible to cut off the water supply while the plate voltage is applied. If the filament voltage is applied in case the element 46 and 47 are used and the temperature of the outgoing water rises to such a degree that one or the other of the thermometers 32 and 33 operates, the power will be cut off in the manner previously described. If the elements 46 and 47 are omitted and the filament current is left on when the cooling water is completely stopped, an alarm will be given by the bell in the manner hereinbefore described.

The amplifier system B alone may be operated as a vacuum tube oscillation generator. For this purpose, it is merely necessary to disconnect the amplifying system A and bring the secondary of transformer 3 adjacent to' one or both coils of the transformer 11 so that a feed-back coupling from the output circuit of the amplifier B to the input circuit may be secured. Any other known method of coupling the output circuit of a vacuum tube to the input circuit for the purpose of generating oscillations may be employed. The amplifier system A may also be used as an oscillation generator by coupling its output circuit to a suitable tuned circuit and coupling the tuned circuit back to the input circuit. The amplifiers A and B together may also be used as an oscillation generator by coupling the antenna circuit C to the input of the amplifier A. In this case, the tuning of the antenna circuit will be the principal factor in determining the frequency of oscillation. The various features of this invention, are, for the most part, equally applicable to vacuum tube systems operating to modulate high power carrier waves as well as to amplify modulated waves already produced. The transformer 3 is indicated with an iron core. It has a specially designed iron core adapted for radio frequency transformation but an air core transformer may be used.

Having described one form of the invention, the novel features believed to be inherent therein are pointed out in the appended claims.

WVhat is claimed is:

1. A fluid cooled vacuum tube system comprising several tubes with cooling fluid circulating about their anodes, a metallic pipe system serving as a conduit for the liquid, each anode being separated from said metallic pipe system by a short length of conduitof insulating material, through which the fluid flows, said short length with its contained'fluid comprising a resistance of suflicient value to allow the space current of each of said tubes to be measured independently of the space currents of the other tubes.

2. A vacuum tube system having anodes cooled by circulating high resistance fluid, said anodes being at a high potential with respect to ground, and means for insulating said anodes from. the main body of said fluid supply consisting of insulating tubing of sufficient length to form a very high resistance, a metallic piping system for carrying said fluid to and from said tube and said anodes, branch pipes from said piping system to the cooling chamber of each anode, and a short length of insulating'tubing in each of said branch pipes having a relatively low, but substantial resistance.

3. A water cooled vacuum tube system comprising several tubes with cooling water circulating about their anodes, said anodes being encased in individual water jackets, a metallic pipe system serving as conduit for the water, each jacket being separated from said metallic pipe system by a short length of conduit of insulating material through which the water flows, said short length with its contained fluid comprising a resistance of sufiicient value to allow the space current of each of said tubes to be measured independently of the space current of the other tubes.

4. In a signaling system, the combination of, a discharge device supplied with space current for relaying signaling waves, a'circuit connecting the cathode with ground, including means for separating the direct current and alternating current components of said space current, a time integrating element to indicate the total time during which the discharge device is operated, and means controlled by the direct current component of the space current for rendering said time integrating device operative during operation of the discharge device and inoperative at other times.

5. A high power fluid cooled vacuum tube system comprising a supporting framework, a centrally mounted piping system insulatingly mounted on the framework, a plurality of vacuum tubes having external anodes located in cooling chamber supplied with cooling fluid by the piping system, and fluid inlet and outlet means for the piping system comprising a hose coil wound upon a cen trally mounted insulated support.

6. A modulation indicating device for an amplifier of the vacuum tube type which repeats modulated waves and partially rec tifies high frequency waves to produce alternating waves of a frequency corresponding to the amplitude variation frequency of the amplified wave, comprising an indicating device included in a path in shunt to a portion of the space current circuit of the amplifier, said path being of low impedance to said partially rectified waves.

7. In a vacuum tube wave transmitting system, a plurality of high power tubes, a

plate circuit common to all said tubes, and

means caused to operate when the plate current is turned on and which operates only ment current is turned on and Wlll'lll operates only While the filament current is on, from which may be determined the total time during a given period during which the filament circuit is. energized.

In WltDGSS whereof, I hereunto subscribe my name this 22nd day of May, A. I). 1922.

' ARTHUR A. ()SYVALD. 

